Improvement in pistons for steam-engines



UNITED STATES PATENT OEEicE.

NATHAN I). STEVENS, OF BOSTON, MASSACHUSETTS.

IMPROVEMENT IN PISTONS FOR STEAM-ENGINES.

Specification forming part of Letters Patent No. 44,674, dated October11, 1864.

Cylinders; and I do hereby declare the same to be fully described in thefollowing specitication, and represented in the accompanying drawings,ot' which- Figure l is a side view, and Figs. 2 and 3 transversesections, of a piston-head provided with my invention, Fig. 2 beingtaken in a plane in line with the axis of the head, while Fig. 8 istaken in a plane cutting the said plane at right angles and goingthrough the ring and its groove, to be hereinafter described.

My improvement has reference to an enginepiston provided with one ormore metallic packing-rings. As the head of such a piston is usuallymade, it is not only provided with one or more steam-passages leadingthrough its opposite ends and into a steam chamber or space within it,(the heath) but it also has one or more passages leading through itscircumi'erence and into the ring-space thereof, the same bein g in orderthat the steam of the cylinder may enter the chamber through the plssageor passages in its end or ends, and pass from such chamber into thering, groove, or space, and act against the packing-rung in order toexpand it.

In carrying out my invention in whole I have a close chamber within thepiston-head* that is, such chamber has no opening leading through eitherof the ends of the piston by which steam from the cylinder can passthrough such end and into the chamber, but it has one or more openingsleading out of it and into the ring space or groove. Furthermore, thering has a width a very little less than that of its groove, in orderthat steam may pass between one side of the y ring and one side of thegroove,and thence such an interval, which is caused by the exhaust-portbeing opened before the receivingport is opened. After the exhaust-porthas been opened the piston-head still has to travel a short distance erethe steam is next brought Vagainst it, and were the ring not keptexpanded by the steam in the close chamber the steam, when entering thecylinder, would expand the ring suddenly and be liable to break orotherwise injure it. While the piston is in the act ot' being driven bythe steam part of such steam will be entering the close chamber, the ring being expanded by the stealn. The ring will first be expanded by thesteam passing into the groove of the said ring, after which, and whilethe piston may be moving in its stroke, the steam will pass into theclose chamber, it entering the chamber through the opening leading intoit from ,the ring-groove. This steam will not be lost from the closechamber immediately when the'exhaust takes place, for it requires aninterval of time for it to get out of the chamber, corresponding to thatwhich was required for it to get into such chamber. Now, this .intervalis longer than the period which intervenes between the exhaust of thesteam on one end of the piston and its introduction to the other end.Oonsequently the expansive power of steam within the close chamber ofthe head will operate to keep the ring expanded, and thus prevent itstoo sudden expansion by the entering steam.

In the drawings, A denotes the piston-head, within the circumference ofwhich there is a groove, a, for holding an annulus or ring, b, bothgroove and ring being either square or rectangular in cross-section.

In the bottom of the groove a there is an annular projection, c, whichgoes around the entire head. A small opening or passage, d, leads fromthe ringgroove directly into a close chamber, e, made within thepiston-head. The ring is cut open at its lower part, each end of thering being formed with a semicircular notch to abut against and embracea curved pin, j', which is inserted in the pistonhead and serves toprevent the ring from revolving around within the ring-groove of thehead. The hole or passage d may have a diameter somewhat greater thanthe width of the projection c, in order that the steam may be able toenter the passage. The object of the annular projection is to preventtle month of the passage d from becoming closed by the ring, which wouldbe likely to occur Were there no such projection. Thus, the projectioninsures the entrance of the steam into the passage d. With a pistonh badso made, only one packing-ring` becomes necessary, and this will be keptproperly eX- panded during,` the entire stroke ofthe piston. Thepacking-ring, by being of a less Width than the groove, will vibratetherein or first be forced to one side of the groove during,` one strokeof the piston, and next be forced against the other side of the grooveduring the next stroke of the piston. This n ill enable the steam to getunder the ring so as t0 expand it; therefore I claiml. The improvedpiston or piston-head, as made With the vil ratory ring and its groove,

land the steam-tight chamber opening into the

